Low-sugar yogurt making by the co-cultivation of Lactobacillus plantarum WCFS1 with yogurt starter cultures

Yogurt making traditionally relies on the simultaneous utilization of 2 starters: Streptococcus thermophilus and Lactobacillus bulgaricus, but these 2 strains normally metabolize the glucose portion of lactose and release galactose into extracellular medium, resulting in high levels of residual galactose and unfermented lactose in yogurt, which leads to several industrial and health concerns. In this study, we found that Lactobacillus plantarum could effectively metabolize both lactose and galactose. Comparative genomic analysis demonstrated the constant presence of a chromosome-encoded Leloir pathway for galactose metabolism in Lb. plantarum species, and the gal operon was driven by a strong constitutive promoter in Lb. plantarum WCFS1, displaying great potential in low-sugar yogurt making. To test this hypothesis, Lb. plantarum WCFS1 was co-cultured with S. thermophilus or Lb. bulgaricus in lactose-based medium. Results showed that lactose was consumed completely and galactose was metabolized efficiently. For yogurt making, co-cultivation of Lb. plantarum WCFS1 with yogurt starter cultures produced a higher reduction of total sugar content compared with the traditional fermentation processes. In addition, the sensory analysis indicated that the yogurt fermented with yogurt starter cultures and Lb. plantarum WCFS1 was acceptable to consumers in appearance, texture, and flavor. Therefore, this study emphasized the potential to manufacture low-sugar yogurt by the co-cultivation of Lb. plantarum with yogurt starter cultures.